1. Field of the Invention
The present invention relates to a method for continuously processing an organic solvent-containing air discharged from a production process, while supplying a dehumidified air to the production process. More particularly, the invention comprises simultaneously and continuously carrying out a dehumidification step of dehumidifying an air to be supplied to a production process by a dehumidifying member on which a dehumidification agent is supported, a dehumidifying member-regeneration step of regenerating the dehumidifying member which has adsorbed moisture, an adsorbing-removing step of removing organic solvents in the air to be processed by adsorbing the organic solvents in an adsorbing member containing an adsorbent such as zeolite supported thereon, an adsorbing member-regenerating step of regenerating the adsorbing member which has adsorbed the organic solvents, and a combustion step of burning the organic solvents in the air containing high-concentration organic solvents produced by regenerating the adsorbing member.
2. Description of Related Art
In production processes for manufacturing liquid crystals, semiconductors, LEDs, plasma displays, resins, coating materials, and the like and facilities for carrying out printing, coating, cleaning, and the like (hereinafter referred to from time to time as “production processes”), an external air and the like are dehumidified using a dehumidifying member to supply dehumidified air to the production processes and, at the same time, air containing organic solvents such as a halogenated hydrocarbon, toluene, and ethyl acetate (hereinafter referred to from time to time as “organic solvent-containing air”) is discharged from the production processes. Since such organic solvents are harmful, the organic solvents in the air discharged from these processes must be removed by an appropriate method.
A conventional method for processing an organic solvent-containing air comprises an adsorbing-removing step of removing the organic solvents in the air by causing the air to flow through an adsorbing member, an adsorbing member-regenerating step of regenerating the adsorbing member by causing a regeneration air to flow though the adsorbing member which has adsorbed the organic solvents, and a combustion step of feeding a concentrated air produced in the adsorbing member-regeneration step to a combustion furnace and burning the organic solvents in the concentrated air. The adsorbing-removing step, regeneration step, and combustion step are carried out simultaneously and continuously using an adsorption apparatus equipped with an adsorbing member containing an adsorbent such as zeolite supported thereon and a processing system for an organic solvent-containing air equipped with a combustion furnace packed with an oxidation catalyst.
A conventional method for processing an organic solvent-containing air will be described with reference to FIG. 5. FIG. 5 is a flow chart showing a conventional method for processing an organic solvent-containing air. A conventional processing system 50 for an organic solvent-containing air shown in FIG. 5 has an adsorber 51, which is equipped with an adsorbing member divided into an adsorption zone and a regenerating zone, and a combustion furnace 52 packed with an oxidation catalyst. In the adsorber 51, the organic solvents in the air M to be processed are adsorbed and removed in the adsorption zone and, at the same time, the adsorbing member which has adsorbed the organic solvents is regenerated in the regeneration zone. The adsorbing member-regeneration air P used for regenerating the adsorbing member is discharged from the adsorber 51 as a concentrated air containing high-concentration organic solvents. The concentrated air is supplied to the combustion furnace 52 via a concentrated air feed pipe 53. The organic solvents in the concentrated air are burnt in the combustion furnace 52 to remove the organic solvents in the concentrated air and an exhaust gas Q is discharged from the combustion furnace 52.
In this manner, in the conventional method of processing an organic solvent-containing air, an adsorption-treated air N produced by processing an air G to be processed in the adsorber 51 and the exhaust gas Q from the combustion furnace are discharged to the atmosphere.
Because the organic solvents burn by being catalyzed with an oxidation catalyst in the combustion furnace, an enormous heat is generated and the oxidation catalyst is exposed to a high temperature. Since a platinum catalyst, of which the upper limit of the operating temperature is 500° C., is commonly used as the oxidation catalyst, if heated above 500° C., the oxidation catalyst decreases its performance due to deterioration by heat. Therefore, it is necessary to control the temperature of the oxidation catalyst in a range not exceeding 500° C. The temperature of the oxidation catalyst is controlled by detecting the temperature of the combustion furnace exhaust gas and adjusting the temperature of the air supplied to the combustion furnace according to the temperature of the exhaust gas. The temperature of the air supplied to the combustion furnace is usually in a range of 250° C. to 300° C.
The organic solvents can be burnt only incompletely in the combustion furnace if the concentration of the organic solvents in the air supplied to the combustion furnace is too high. That is, there is an upper limit to the concentration (content) of the organic solvents in the air which can be processed by the combustion furnace.
It is natural that the concentration of the organic solvents in the organic solvent-containing air discharged from the production processes and the like, namely, the concentration of the organic solvents in the air to be processed, fluctuates. If the concentration of the organic solvents in the air to be processed increases, the concentration of the organic solvents in the air processed in the combustion furnace also increases. When the increase in the concentration of the organic solvents in the air supplied to the combustion furnace is small, the concentration of the organic solvent can be lowered by introducing external air to reduce the concentration to a level not exceeding the process limit concentration of the combustion furnace. In regard to the fluctuation of the concentration which may cause trouble in the process, an increase of the concentration is so great that the concentration of the organic solvents must be reduced by introducing a great amount of external air. However, since there is a limitation to the throughput of a combustion furnace, the amount of external air to be introduced is limited. Thus, the problem could not be obviated in some cases by introducing an external air.
In such a case, an organic solvent-containing air with a concentration exceeding the process limit concentration of the combustion furnace is supplied to the combustion furnace. It is impossible for the combustion furnace alone to completely burn the organic solvent, in which case an unburned organic solvent may mix into the combustion furnace exhaust gas. For this reason, an exhaust gas containing an unburned organic solvent may be emitted into the atmosphere from the combustion furnace.
Moreover, since the combustion furnace exhaust gas may contain the unburned organic solvent even at a high temperature, it was impossible to use the combustion furnace exhaust gas for regenerating the dehumidifying member which has adsorbed moisture. Therefore, an air with a low content of organic solvents, such as an external air, must be heated and caused to flow through the dehumidifying member. For this reason, the conventional method had a problem of extremely poor thermal efficiency.
Accordingly, an object of the present invention is to provide a method for processing an organic solvent-containing air which can be operated in spite of a rapid fluctuation of the concentration of organic solvents in the air to be processed, that is, a method capable of being operated without accompanying an increase in the organic solvent content in the air to be discharged into the atmosphere after processing, even if the concentration of organic solvents rapidly fluctuates, and capable of using a combustion furnace exhaust gas as an air for regenerating dehumidifying member, thereby ensuring high thermal efficiency.